1. Field of the Invention
The invention relates to an electricity storage device in which a case contains an electricity storage unit and a coolant for cooling the electricity storage unit.
2. Description of the Related Art
There is a possibility that, in a battery pack in which a case contains a secondary battery and an insulating oil, heat and gas are produced due to the electrolysis of the electrolyte solution in the secondary battery that is caused by the electricity excessively supplied when the secondary battery is overcharged, for example. For this reason, there have been developed a battery pack that detects gas produced in the battery pack, and a battery pack that detects the change in pressure in the battery pack that occurs due to produced gas, in order to determine whether the battery pack (secondary battery) is in an abnormal state. A battery pack is also available in which, when it is detected that gas is produced, appropriate control is performed according to the abnormality that occurs in the secondary battery (see Japanese Patent No. 3638102, for example).
A battery pack is also available that has a mechanism for discharging gas produced by the secondary battery to the outside of the battery pack (see Japanese Patent Application Publication No. 63-98953 (JP-A-63-98953) (FIGS. 1 and 2), Japanese Utility Model Publication No. 61-42283 (JP-UM-A-61-42283) (FIG. 1), and Japanese Utility Model Application Publication No. 63-61758 (JP-UM-A-63-61758) (FIGS. 1 and 2), for example).
However, Japanese Patent No. 3638102 includes no disclosure concerning a configuration in which gas produced in a secondary battery is efficiently led to a predetermined position (the position at which a gas sensor for detecting gas is positioned, for example). Thus, there is a possibility that the accuracy of detection by the gas sensor can be insufficient.
In a device described in JP-A-63-98953, the lid of a battery case has an oblique surface to lead the gas produced by a cell to a predetermined position (a portion to which a gas-discharge helping device is connected). In this configuration, however, the device is designed so that an insulating oil is brought into contact with the oblique surface of the battery case lid, which causes the following problem.
In the case where, in producing a battery pack, the battery case is enclosed by the lid thereof after a secondary battery and an insulating oil are contained in the battery case, if the battery case lid has the oblique surface as described in JP-A-63-98953, it is required to add the insulating oil to bring the battery case lid into contact with the insulating oil after fixing the battery case lid to the battery case. In this case, the assembly operation of the battery pack becomes complicated.